Coexpression of cytokeratins typical for columnar and squamous differentiation in sinonasal inverted papillomas

Cytokeratin (CK) expression was studied in 22 sinonasal inverted papillomas . Columnar (respiratory) epithelium in inverted papillomas abundantly expre ssed CK7, CK8, CK18, and CK19. Immunoreactivity for CK5/14 and CK17 was fou nd in basal and parabasal/suprabasal cells. Transitional (cuboidal) and squ amous epithelium in inverted papillomas comparably expressed CK7, CK8, CK18 , and CK19. In addition CK13 was found in subluminal and surface cells. Imm unoreactivity for CK5/14 and CK17 involved all layers of the epithelium. In nonpapillomatous nasal mucosa adjacent to inverted papillomas. CK expressi on in columnar (respiratory) epithelium exactly matched the findings in inv erted papillomas. Transitional (cuboidal) and squamous epithelium in nonpap illomatous mucosa were negative for CK7, CK8, CK18, and CK19. CK13 was expr essed in subluminal and surface cells. Immunoreactivity for CK5/14 and CK17 was restricted to basal and parabasal/suprabasal cells. Conclusively, tran sitional (cuboidal) and squamous epithelium in inverted papillomas but not in the adjacent mucosa coexpress CKs typical for columnar and squamous diff erentiation.